1. Technical Field
The present disclosure relates to vehicle power transmission units, and, more particularly, to remotely-actuatable multispeed transmission units.
2. Description of the Related Art
Large industrial machinery systems, such as earth moving equipment and other construction vehicles and apparatuses, may use individual power transmission units mounted at the system's driven endpoint. For example, gear reduction units mounted at the hub of each driven wheel can convert the relatively high rotational speeds of driven input shafts into lower rotation speeds, thereby accommodating the large-diameter wheels, heavy loads and low speeds frequently encountered by heavy duty construction vehicles. In another example, independent gear reduction units may be used in drilling devices such as earth augers, in order to provide the low-speed, high-torque auger rotation needed for drilling holes in tightly packed soil.
Such individual power transmission units are sometimes referred to as drive units, and include a housing which encases a transmission linking an external power source to a driven unit. Where the power source is external (e.g., a vehicle motor and/or primary vehicle transmission), the drive unit may be referred to as a nonintegrated drive unit. Alternatively, integrated drive units include an integral power input device, such as an attached hydraulic motor. For example, integrated drive units may utilize a hydraulic motor which is linked to the drive unit via a motor output shaft coupled to an input shaft of the drive unit. The drive unit has its own output shaft or output hub which links to the driven unit (such as a wheel or auger as noted above). For the purposes of the present disclosure, “drive unit” generically refers to both nonintegrated and integrated drive units.
In some cases, multispeed drive units capable of shifting between varying levels of gear reduction may be desirable. For example, in the case of heavy duty construction vehicles, a drive unit having high and low gear reduction configurations may be provided. The high gear reduction configuration provides low-speed, high-torque power transmission, such as for uneven terrain at a construction site. The low gear reduction configuration provides higher potential wheel rotation speeds, such as for driving the vehicle on maintained roads. In the case of industrial augers, the high-torque, low-speed mode (i.e., the high gear reduction configuration) may be used for drilling and deepening holes in the earth, while the lower-torque, higher-speed mode (i.e., the low-reduction configuration) may be used for quickly extracting the auger bit from a drilled hole and dislodging soil from the surface of the drill bit.
Substantial design efforts have focused on providing multispeed drive units which can be easily toggled between low and high gear reduction values. For example, hydraulically actuated wheel drive units may employ multiple hydraulic actuators which operate to engage and/or disengage internal gearing mechanisms to toggle between high- and low-reduction configurations (such as by toggling clutch mechanisms between engaged and disengaged configurations). However, such multi-actuator drive unit designs require careful synchronization of the various actuators to function properly, with the attendant cost and system complexity associated with such synchronization.
Other designs may include a mechanical shift, such as a movable or translatable gear which selectively engages higher or lower gear reduction assemblies depending on the physical location of the movable gear. However, such mechanical shift drive units require that the driven unit be stopped prior to toggling the movable gear, and may require that internal pressures on the movable gear be relieved prior to such toggling.